The correct answer is A) No change in color (remaining at red with a pH of 2.0). When circulating heated sulfuric acid through a feed water heater to remove scale, the lack of color change (remaining red) and continued low pH (around 2.0) indicates that the scale has been successfully removed. The red color and low pH are characteristic of the sulfuric acid, and if the scale was effectively dissolved, these properties would remain unchanged. The other answer choices are incorrect because a change in color to orange with a higher pH of 4.0 (option D) would indicate that the acid has been neutralized, meaning the scale removal was not complete. Options B and C do not accurately describe the expected results of this scale removal process.